Photoelectric conversion device using TiOF2 as semiconductor

ABSTRACT

Use of TiOF 2  as semiconductor in a photoelectric conversion device, in particular in a dye-sensitized solar cell. A photoelectric conversion device, in particular a dye-sensitized solar cell, comprising a semiconductor layer containing at least TiOF 2 . The TiOF 2  is preferably used in the form of nanoparticles. Dyes, method(s) of making them, and their use in photoelectric conversion devices, especially in dye-sensitized solar cells. A dye-sensitized solar cell comprising at least one fluorinated compound as a dye and at least TiOF 2  as semiconductor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application no.PCT/EP2012/050502 filed Jan. 13, 2012, which claims priority to U.S.provisional application No. 61/433,179 filed on Jan. 14, 2011 and toEuropean application No. 11170427.6 filed on Jun. 17, 2011, the wholecontent of each of these applications being incorporated herein byreference for all purposes.

TECHNICAL FIELD

The present invention relates to dye compounds, in particular dyecompounds based on phthalocyanine and naphthalocyanine analogues, moreparticularly on fluorinated phthalocyanine analogues, method(s) ofmaking them, and their use as dyes in photoelectric conversion devices,especially in dye-sensitized solar cells (DSSC).

BACKGROUND OF THE INVENTION

Conventional solar cells convert light into electricity by exploitingthe photovoltaic effect that exists at semiconductor junctions. In otherwords, the commercial solar cells absorb energy from visible light andconverts excited charge carriers thereof to electric energy. At present,the main commercial solar cells are silicon-based solar cells. For asilicon-based solar cell, there are shortcomings in that high energycosts for material processing is required and many problems to beaddressed such as environmental burdens and cost and material supplylimitations are involved. For an amorphous silicon solar cell, there arealso shortcomings in that energy conversion efficiency decreases whenused for a long time due to deterioration in a short period.

Recently, many attempts have been undertaken to develop low-cost organicsolar cells, whereby development of one particular type of solar cellwhich is a dye-sensitized solar cell (DSSC) is accelerated that is aclass of thin film solar cells, is based on a semiconductor formedbetween a photo-sensitized anode and an electrolyte, and generally usesan organic dye to absorb incoming light to produce excited electrons.

The DSSC offers the prospect of a cheap and versatile technology forlarge scale production of solar cells. The dye-sensitized solar cell(DSSC) is formed by a combination of organic and inorganic componentsthat could be produced at a low cost. The dye-sensitized solar cellshave advantages over silicon-based solar cells in terms of simplifiedprocessing steps, low fabrication cost, transparency and pleochroism.The dye-sensitized solar cells can be fabricated from flexiblesubstrates to function as cells of mobility and portability.Dye-sensitized solar cells have also the advantage to be lightweight.

The dye-sensitized solar cells have lower energy (photoelectric)conversion efficiency over that of the silicon-based solar cells suchthat a wide range of researches are briskly under way to enhance theenergy conversion efficiency. In order to improve the energy conversionefficiency, extension of wave length up to infrared regions is beingwaged with great concern. It is known that the energy bandgap (eV) foruse in solar cells must exceed 1.4 eV (electron volt).

The basic element of a DSSC is generally a TiO₂ (titanium dioxide)nanoparticulate structure sensitized with dye molecules to form its coreof a DSSC. The assembly of titanium dioxide nanoparticles is wellconnected to their neighbors. TiO₂ is the preferred material for thenanoparticles since its surface is highly resistant to the continuedelectron transfer. However, TiO₂ only absorbs a small fraction of thesolar photons (those in the UV). The dye molecules attached to thesemiconductor surface are used to harvest a great portion of the solarlight.

The main dye molecules consist on one metal atom and a large organicstructure that provides the required properties (wide absorption range,fast electron injection, and stability), such as ruthenium complexes.The dye is sensible to the visible light. The light creates andexcitation in the dye that consists on a highly energetic electron,which is rapidly injected to the semiconductor (usually TiO₂)nanoparticles. The nanoparticulate semiconductor functions as thetransporter of light induced electrons towards the external contact, atransparent conductor that lies at the basis of the semiconductor(usually TiO₂) film.

Meanwhile, phthalocyanine is an intensely colored macrocyclic compoundthat is widely used in dyeing. Phthalocyanines form coordinationcomplexes with most elements of the periodic table. These complexes arealso intensely colored and also are used as dyes. Approximately 25% ofall artificial organic pigments are phthalocyanine derivatives.

Phthalocyanine (Pc) compound used as a dye in electrodes for solar cellshas advantages such as high transmittivity relative to visible light,excellent selective absorption power in the near infrared region, highheat resistance, high weatherability and high thermotolerance, so thatthe phthalocyanine compound has a wide range of applications.

For instance, the use of zinc phthalocyanines in DSSCs has beendisclosed by Md. Nazeeruddin et al., Angew. Chem. Int. Ed., 2007, 46,373-376 and by M. Grätzel et al., Solar Energy Materials & Solar Cells,2007, 91, 1611-1617.

However, there is still a need for dyes that could lead to animprovement of DSSCs, in particular to improved conversion efficiency.More particularly, there is still a need for dyes exhibiting a broadspectrum of adsorbed light (i.e. absorbing as much of the solar spectrumas possible), a high molar extinction coefficient, contributing to thelong-term stability of the device and/or allowing an improved conversionefficiency.

SUMMARY

In view of the above, the purpose of the present invention is to providenew dyes showing particularly advantageous properties when used inphotoelectric conversion devices, in particular in dye sensitized solarcells (DSSC), especially an improved conversion efficiency of thedevices or cells More particularly, the purpose of the present inventionis to provide new dyes having a broad absorption spectrum, particularlyin the visible and near-IR regions, i.e. absorbing as much of the solarspectrum as possible. The new dyes of the present invention should alsoexhibit a high molar extinction coefficient. Therefore phthalocyanineand naphthalocyanine analogues absorbing up to around 850 nm with highextinction coefficients of >10⁵ L mol⁻¹ cm⁻¹ are used. Such dyes shouldpreferably exhibit the very high or even higher electron injection speedinto a semiconductor as previous dyes and generally have an improvedcommunication and directionality of the electrons when being transferredfrom the sensitizer to the semiconductor electrode. Such dyes shouldalso contribute to the long-term stability of such devices, for example,better resistance to water contained in trace amounts in the devices andbetter shielding of the Ti-electrode against corrosion throughcomponents present in the electrolyte, such as the triiodide/iodidecouple. The dyes should also be anchored and/or persistently attached tothe semiconductor surface and/or to the surface of the photoelectrode.The attachment should be such that the dye stays attached over extendedperiods of several months and preferably years.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows the HOMO/LUMO calculated levels for compounds ZnPc 1˜7provided in the Examples.

DETAILED DESCRIPTION

One embodiment of the present invention relates to a compound,especially a dye compound, based on phthalocyanine and naphthalocyanineanalogues, comprising an element M in a macrocyclic structure having aformula (X):

wherein:

-   -   M is 2H (metal free analogue), zinc (Zn(II)), magnesium        (Mg(II)), Al(III)X, Si(IV)X₂, Sn(IV)X₂ wherein X is selected        from halides, OH and OR with R being an alkyl or aryl group;    -   R₁ is H or an alkyl group substituted by at least one halogen        atom;    -   R₂ is —CN, —COOH or an alkyl group substituted by at least one        halogen atom;    -   R₃ is independently selected from H, F, —C_(n)F_(2n+1), —OR′,        and NR₂′; and    -   R₄ are independently selected from H, F, —C_(n)F_(2n+1), —OR′,        —NR′₂, and from groups forming an optionally substituted        aromatic cycle, adjacent to the external aromatic cycles of the        macrocyclic structure,        with R′ being independently selected from H or alkyl or aryl        groups, optionally fluorinated.

In the compounds of the present invention, M is preferably selected fromzinc (Zn(II)), magnesium (Mg(II)), Al(III)X, Si(IV)X₂, Sn(IV)X₂ whereinX is selected from halides, preferably from F, Cl and Br; morepreferably from Zn(II) and stannous halide (SnHal₂). M may alsoadvantageously be selected from 2H, which corresponds to the metal freeanalogues and which may result also in high excited state life times forefficient electron transfer to the semiconductor.

In the compounds of the present invention, R′ is preferably selectedfrom optionally fluorinated alkyl or aryl groups, more preferably fromperfluorinated alkyl (—C_(n)F_(2n+1)) or aryl groups, for instance from(per)fluorinated methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl andphenyl groups. R′ also can be an optionally substituted terphenyl group,such as alkoxyterphenyl, in particular.

For example, R′ may be selected from the group consisting of methyl,ethyl, n-propyl, i-propyl, n-butyl, t-butyl, phenyl, and theircorresponding perfluorinated groups such as —CF₃, —C₂F₅,heptafluoroisopropyl (—CF(CF₃)₂), or hexafluoroisopropyl (—CH(CF₃)₂).

In the present invention, R₁ may be selected from H and alkyl groupssubstituted by at least one halogen atom, in particular a perhalogenatedalkyl group, for example —CH₂F, —CHF₂, —CF₃, —CF₂Cl, and —C₂F₅. R₁ maymore particularly be selected from H, —CF₃ or —C₂F₅.

In the present invention R₂ may be selected from —CN and alkyl groupssubstituted by at least one halogen atom. A particular example of alkylgroups substituted by at least one halogen atom is a perhalogenatedalkyl group, for instance —CH₂F, —CHF₂, —CF₃, —CF₂Cl, and —C₂F₅. R₂ maymore especially be selected from —CN and —CF₃. In another aspect, R₂ maybe —COOH.

In the compounds of the present invention, R₃ are the same or different,especially the same, and are advantageously selected from—C_(n)F_(2n+1); —OR′, and NR₂′; preferably from —C_(n)F_(2n+1),—OC_(n)H_(2n+1) and —OC_(n)F_(2n+1), for instance

—OCH₃, —OCF₃, —OCF(CF₃)₂, or —OCH(CF₃)₂.

In the compounds of the present invention, R₄ are the same or different,usually the same, and are typically selected from H, F, —C_(n)F_(2n+1),—OR′, and NR₂′;

preferably from —C_(n)F_(2n+1), —OC_(n)H_(2n+1) and —OC_(n)F_(2n+1), forinstance

—OCH₃, —OCF₃, —OCF(CF₃)₂, or —OCH(CF₃)₂. In a more specific embodiment,R₄ are selected from groups forming an optionally substituted aromaticcycle, adjacent to the external aromatic cycles of the macrocyclicstructure. In said more specific embodiment, the aromatic cycle isespecially a C6 aromatic cycle, thus forming a naphthalene moiety withthe benzene moiety of the macrocyclic structure. In this specific case,the compound will be a naphthalocyanine analogue. Said external aromaticcycle may optionally be substituted, especially by halogen atoms, inparticular with F atoms.

In some preferred embodiments, R₁ is —CF₃ or —C₂F₅. In some embodiments,R₁ is H and R₂ is —CN. In some other embodiments, R₂ is —CN, and R₄ isH. In some alternate embodiments, R₂ is —CF₃, and R₄ is H. In some yetalternate embodiments, R₂ is —CF₃, and R₄ is F.

A specific embodiment of the present invention relates to a compoundcomprising an element M in a macrocyclic structure having a formula (X):

wherein:

-   -   M is zinc (Zn) or stannous halide (SnHal2);    -   R₁ is H, —CF₃, or —C₂F₅;    -   R₂ is —CF₃, —COOH or —CN;    -   R₃ is —OCF₃, —OCH₃, or

and

-   -   R₄ is H or F.

In this specific embodiment, R₂ may be CF₃ or —CN. In another aspect ofthis specific embodiment, R₂ is —COOH.

Any substituted benzene, for instance methoxy or fluoromethoxy benzenes,can be combined with any thiophene moiety mentioned hereafter. In anespecially advantageous embodiment, methoxy benzenes or combined withany thiophene moiety. In another especially advantageous embodiment,fluorinated benzenes are combined with a fluorinated thiophene moiety.

Another embodiment of the present invention relates to a compoundcomprising the element M (same as defined above) in a macrocyclicstructure having a similar formula than formula (X), but which comprisesmore than one thiophenic moiety.

A preferred compound according to the present invention, comprising theelement M (same as defined above), has a structure of formula beingselected from the group consisting of:

preferably from Structure I, II, V, VI, X and XII.

Any of the compounds of the present invention described herein is a dyewhich is suitable for use photoelectric conversion devices, especiallyin dye-sensitized solar cells (DSSC).

The present invention also relates to the use of TiOF₂ (titanyloxyfluoride, titanium oxyfluoride or titanium fluoride oxide) assemiconductor in a photoelectric conversion device, in particular in adye sensitized solar cell. TiOF₂ has the conduction band level at lowerenergy compared to TiO₂ which should improve the photo-induced electrontransfer from the excited dye to the semiconductor. The presentinvention therefore also relates to a photoelectric conversion device,in particular a dye sensitized solar cell (DSSC), comprising asemiconductor layer containing at least TiOF₂ on a transparentconducting glass electrode (e.g. F doped SnO₂ as conducting material).The TiOF₂ is preferably used in the form of TiOF₂ nanoparticles, inparticular TiOF₂ particles having a mean primary particle size from 15to 50 nm. The layer thickness is typically from 500 nm to 10 um. TheTiOF₂ may be used as the sole semiconductor in the DSSC semiconductorlayer or may be combined in mixture with any other suitablesemiconductor compound, for instance TiO₂. Another possibility is tohave at first a dense TiO₂ layer on the conducting glass followed by ananoporous TiOF₂ layer.

Fluorinated compounds according to the present invention are especiallyadvantageous, in particular when combined with TiOF₂ used assemiconductor in dye sensitized solar cells. Indeed, without being boundby any theory, it is believed that the conduction band edge of TiOF₂ islower in energy compared to the conduction band of TiO₂ while thefluorinated compounds of the present invention exhibit a lower LUMOlevel compared to similar non-fluorinated compounds. Such combination isthus especially advantageous.

The present invention further relates to a photoelectric conversiondevice, preferably a dye-sensitized solar cell, which comprises thecompound of the present invention. The compound of the present inventionis used as a dye, in particular as a sensitizing dye, in such device orcell.

In a preferred embodiment, the present invention relates to adye-sensitized solar cell comprising at least one fluorinated compoundaccording to the present invention as a dye and at least TiOF₂ assemiconductor. The fluorinated compound according to the presentinvention may be fluorinated via at least part of its R₁, R₂, R₃ or R₄groups. The fluorinated compound according to the present invention mayfor instance be selected from any compound of Structure I to XXIXwherein R₁ is selected from halogenated groups as defined above,especially from any compound of Structure II, III, IV, V, VI, VII, VIII,XI, VII and VIII, more particularly from any compound of Structure II,III, IV, V and VI.

The present invention further relates to a method for making theabove-mentioned compounds. The method comprises utilizing one or morearomatic dinitriles, for instance fluorinated alkoxyphthalonitriles, andone or more thiophenes as building blocks for the macrocyclic structure.The method may further comprise utilizing an M-containing precursor. Thepresent invention further relates to a compound obtained by such method.The aromatic dinitriles may be selected, for example, from the groupconsisting of aryloxyphthalonitriles, aryloxynaphthalonitriles,alkylthiophthalonitriles and alkylthionaphthalonitriles.

The thiophene used in the preparation of the compounds of the presentinvention is preferably fluorinated.

In the method of the present invention, it is especially advantageous touse a fluorinated phthalonitrile or a fluorinated alkoxyphthalonitrileand a fluorinated 2,3-dicyanothiophene as building blocks for thepreparation of the macrocyclic structure.

The method may comprise using a single aromatic dinitrile (for instancea fluorinated alkoxyphthalonitrile) building block (one formula);alternatively the method may comprise using two or more aromaticdinitriles (for instance fluorinated alkoxyphthalonitriles) of differentformulae. The method may comprise using a single thiophene buildingblock; alternatively the method may comprise using two or more thiophenebuilding blocks of different formulae, including a mixture of 2,3- and3,4-dicyanothiophenes.

Aromatic dinitriles for manufacturing the compounds of the presentinvention may be selected from any suitably substituted aromaticdinitriles of following formula:

wherein R₃ and R₄ have the same meaning as defined above for compound offormula (X). In particular, the aromatic dinitriles may be selected fromsuitably substituted phthalonitriles and naphthalodinitriles, includingamong others alkoxyphthalonitriles, aminophthalonitriles,amino-alkoxyphthalonitriles, fluorinated phthalonitriles, fluorinatedalkoxyphthalonitriles, or optionally substituted naphthalodinitrilessuch as alkoxy naphthalodinitriles, fluorinated naphthalodinitriles, orfluorinated alkoxy naphthalodinitriles.

Suitable alkoxyphthalonitriles may for instance be selected fromcompounds of following formula (A):

wherein R′ has the same meaning as defined above for compound of formula(X). R′ may for instance be selected from optionally fluorinated alkylor aryl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl,i-butyl, t-butyl, phenyl and their corresponding perfluorinated groupssuch as —CF₃, —C₂F₅, or hexafluoroisopropyl (—CH(CF₃)₂).

Suitable aminophthalonitriles may be selected from compounds offollowing formula (B):

wherein R′ has the same meaning as defined above for compound of formula(X). R′ may for example be selected from alkyl and aryl groups such asmethyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl and phenylgroups. The aminophthalonitriles are preferably from 4- and4,5-substituted phthalonitriles.

Amino-alkoxyphthalonitriles of following formula (C) may also suitablybe used in the present method:

wherein R′ has the same meaning as defined above for compound of formula(X) and more preferably the same meaning as defined for compounds offormula (A) for the —OR′ group and of formula (B) for the NR′₂ group.

Suitable fluorinated phthalonitriles and fluorinatedalkoxyphthalonitriles may be selected from the group consisting of:

preferably from (D), (E), (G), (H), and (J).

Suitable alkoxy naphthalodinitriles are for instance compounds offollowing formula (M):

wherein R′ has the same meaning as defined above for compound of formula(X). R′ may for instance be selected from optionally fluorinated alkylor aryl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl,i-butyl, t-butyl, phenyl and their corresponding perfluorinated groupssuch as —CF₃, —C₂F₅, heptafluoroisopropyl (—CF(CF₃)₂), orhexafluoroisopropyl (—CH(CF₃)₂), more preferably from methyl, ethyl,t-butyl, phenyl, heptafluoroisopropyl (—CF(CF₃)₂), andhexafluoroisopropyl (—CH(CF₃)₂) groups, most preferably methyl,heptafluoroisopropyl (—CF(CF₃)₂), and hexafluoroisopropyl (—CH(CF₃)₂)groups.

Suitable fluorinated alkoxy naphthalodinitriles are for instancecompounds of following formulas:

wherein R′ has the same meaning as defined above for compound of formula(X). R′ may for instance be selected from optionally fluorinated alkylor aryl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl,i-butyl, t-butyl, phenyl and their corresponding perfluorinated groupssuch as —CF₃, —C₂F₅, heptafluoroisopropyl (—CF(CF₃)₂), orhexafluoroisopropyl (—CH(CF₃)₂), more preferably from methyl, ethyl,t-butyl, phenyl, heptafluoroisopropyl (—CF(CF₃)₂), andhexafluoroisopropyl (—CH(CF₃)₂) groups, most preferably methyl,heptafluoroisopropyl (—CF(CF₃)₂), and hexafluoroisopropyl (—CH(CF₃)₂)groups.

Suitable fluorinated naphthalodinitriles are for example compounds offollowing formula:

Suitable aryloxyphthalonitriles are for example compounds of followingformula:

Suitable aryloxynaphthalonitriles are for example compounds of followingformula:

Suitable alkylthiophthalonitriles are for example compounds of followingformula:

wherein R′ has the same meaning as defined above for compound of formula(X).

Suitable alkylthionaphthalonitriles are for example compounds offollowing formula:

wherein R′ has the same meaning as defined above for compound of formula(X).

The alkoxyphthalonitrile of formula (A) may be prepared as follows,starting from commercially available 2,3-dicyanohydroquinone:

The aminophthalonitrile of formula (B) may be prepared as follows,starting from commercially available 3-nitro or 4-nitrophthalonitrile:

The amino-alkoxyphthalonitrile of formula (C) may be prepared, forexample, by reacting 1,2-dibromo-3-methoxy-5-nitrobenzene with CuCN toform 3-methoxy-5-nitrophthalonitrile which is then treated with asecondary amine to obtain 3-methoxy-5-dialkylaminophthalonitrile.

The fluorinated alkoxyphthalonitrile of formula (D) may be prepared asfollows:

The fluorinated alkoxyphthalonitrile of formula (E) may be prepared asfollows:

wherein CDFA means chlorodifluoroacetic acid and wherein CDFA derivativeis for instance the acid chloride derivative.

The fluorinated alkoxyphthalonitrile of formula (G) may be prepared asfollows:

wherein DMSO means dimethylsulfoxide.

The fluorinated alkoxyphthalonitrile of formula (H) may be prepared asfollows:

The fluorinated alkoxyphthalonitrile of formula (J) may be prepared asfollows:

wherein Red. means reducing agent, for instance H₂, and wherein CDFAmeans chlorodifluoroacetic acid and wherein CDFA derivative is forinstance the acid chloride derivative.

The fluorinated phthalonitrile of formula (L) may be prepared asfollows, starting from commercially available tetrafluorophthalonitrile:

This reaction is preferably conducted at low temperature, for instancearound −78° C.

The alkoxy naphthalodinitrile of formula (M) may be prepared as follows,starting from commercially available 2,3-dicyanonaphthalene-1,4-diol:

Such a reaction is typically conducted in the presence of a base. Thealkoxy naphthalodinitrile of formula (M) might also be prepared byconverting the naphthoquinone precursor with hexafluoroisopropanol underdrying conditions (e.g. with SO₃ or P₂O₅) or by converting thenaphthoquinone precursor with two equivalents of hexafluoropropylenedirectly under radicalar conditions (e.g. in the presence ofazobisisobutyronitrile (AIBN) or light).

The fluorinated alkoxynahthalodinitrile of formula (N) may be preparedas follows:

The fluorinated naphthalodinitriles of formula (Q) and (T) may beprepared follows:

These reactions are preferably conducted at low temperature, forinstance around −78° C.

The aryloxyphthalonitriles of formula (U) may be prepared as follows:

wherein Ts is understood to denote tosyl group.

The aryloxyphthalonitriles of formula (V) may be prepared as follows:

The aryloxynaphthalonitriles of formula (W) may be prepared as follows:

wherein Ts is understood to denote tosyl group and R′ has the samemeaning as defined above for compound of formula (X).

The alkylthiophthalonitriles of formula (X) may be prepared as follows:

wherein Ts is understood to denote tosyl group and R′ has the samemeaning as defined above for compound of formula (X).

The alkylthionaphthalonitriles of formula (Y) may be prepared asfollows:

wherein Ts is understood to denote tosyl group and R′ has the samemeaning as defined above for compound of formula (X).

The thiophene building blocks used in the method of preparation of thecompounds according to the present invention may be selected from thegroup consisting of the following 2,3-dicyanothiophene compounds:

The present invention also concerns the 2,3-dicyanothiophene compoundsof formula (1) to formula (9) described above.

The thiophene building block used in the method for preparing thecompound of the present invention is usually prepared from the followingprecursor:

The thiophene used in the method of preparation may be a fluorinatedthiophene. It may be selected from the group consisting of fluorinatedthiophenes of formula (1), (3), (4), (5) or (6). Also, it may befluorinated thiophenes of formula (8) or (9).

The thiophene may be a ‘F-free’ thiophene of formula (1) or (2).

The “F-free” 2,3-dicyanothiophene of formula (1) or (2) may be preparedby a method comprising the following steps, via precursor (A′):

The “F-free” 2,3-dicyanothiophene of formula (1) or (2) may also beprepared by a method comprising the following steps, via the protectedform of precursor (A′):

The first reaction, between 4,5-dibromothiophene-2-carbaldehyde and CuCNmay for instance be carried out in polar aprotic solvents such as DMF orpyridine.

The thiophene may be a ‘CF₃’ fluorinated thiophene of formula (3) or(4). The fluorinated thiophene of formula (3) or (4) may be prepared bya process employing a thiophene precursor (B′), for instance as follows:

The thiophene precursor (B′) may be prepared by a process comprising thefollowing steps:

The thiophene may be a pentafluorothiophene of formula (5) or (6). Thepentafluorothiophene of formula (5) or (6) may be prepared by a processemploying a thiophene precursor (C′):

The process may comprise steps to prepare the fluorinated thiopheneprecursor (C′) and/or steps to make either the fluorinated thiophene offormula (5) or (6) from the fluorinated thiophene precursor (C′) asfollows:

The dicyanothiophene of formula (7), (8) or (9) may be prepared by amethod comprising the following steps, from the protected form ofprecursor (A′):

Compound of formula CF₃—CO—CH═CH—SH may for instance be prepared byreacting ethoxy-4,4,4-trifluoro-3-buten-2-one (ETFBO, CF₃—CO—CH═CH—OEt)with H₂S or Na₂S.

According to a first embodiment, it is possible to react the thiophenebuilding block with the aromatic dinitrile building block in theoptional presence of a metal salt or derivative of M to form thecompound of the present invention by statistical cyclotetramerization.Such reaction is typically performed by reacting the aromatic dinitrilebuilding block with the thiophene building block in a molar ratio around3:1.

According to a second embodiment, it is possible to first react thearomatic dinitrile building block with a precursor of the thiophenebuilding block, in the presence of a metal salt or derivative of M, bystatistical cyclotetramerization, and to further react the resultingcompound to form the compound of the present invention. In such secondembodiment, the reaction is typically performed by reacting the aromaticdinitrile building block with a precursor of the thiophene buildingblock in a molar ratio around 3:1, in the optional presence of a metalsalt or derivative of M. In said second embodiment, the precursor of thethiophene building block may for instance be selected from precursors(A′), (B′) or (C′) as described above or from corresponding compoundswherein the aldehyde group has been protected by an acetal group. Anexample of corresponding compound for precursor (A′) is shown below:

Such a protected precursor compound may for instance be prepared byreacting precursor compound of formula (A′) with ethylene glycol(HOCH₂—CH₂OH). If such a protected precursor is used, the protectinggroup is then removed to yield the corresponding aldehyde group. Thealdehyde group may then be transformed into the required functionality(i.e. —CH═C(CF₃)(CO₂H) or —CH═C(CN)(CO₂H)), for instance by reactionwith CF₃CH₂CO₂H, CF₃COCO₂H or NCCH₂CO₂H.

In the method of the present invention, the metal salt or derivative ofM may for instance be a Zn salt such as zinc acetate, magnesium oxide,an aluminum derivative such as aluminum chloride or bromide, a siliconderivative such as tetrachlorosilane, or a stannous halide (SnHal₂) suchas tin dichloride (TiCl₂).

The compound of the present invention may be further isolated, forinstance by column chromatography, preferably by high pressure liquidchromatography (HPLC).

While preferred embodiments of this invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit or teaching of this invention. Theembodiments described herein are exemplary only and are not limiting.Many variations and modifications of systems and methods are possibleand are within the scope of the invention. Accordingly, the scope ofprotection is not limited to the embodiments described herein, but isonly limited by the claims that follow, the scope of which shall includeall equivalents of the subject matter of the claims.

Should the disclosure of any patents, patent applications, andpublications which are incorporated herein by reference conflict withthe description of the present application to the extent that it mayrender a term unclear, the present description shall take precedence.

Examples HOMO/LUMO Calculations

HOMO/LUMO calculations were performed using program Hyperchem, Release4.5, PM3 method, gradient 10 exp−3, next lowest RHF.

FIG. 1 summarizes the HOMO/LUMO calculated levels for the followingcompounds:

-   -   ZnPc 1: unsubstituted zinc phthalocyanine;    -   ZnPc 2: compound of formula (X) wherein R1=R3=R4=H and R2=CN;    -   ZnPc 3: compound of formula (X) wherein R1=R3=R4=H and R2=CF₃;    -   ZnPc 4: compound Ia with R1=H (i.e. compound of formula (X)        wherein R1=R4=H, R2=CN, and R3=OCH₃);    -   ZnPc 5: compound Va with R1=H (i.e. compound of formula (X)        wherein R1=R4=H, R2=CF₃, and R3=OCH₃);    -   ZnPc 6: compound VIa with R1=H (i.e. compound of formula (X)        wherein R1=R4=H, R2=CF₃, and R3=OCF₃);    -   ZnPc 7: compound XIIIa with R1=H (i.e. compound of formula (X)        wherein R1=H, R2=CN; R3=F, and R4=CF(CF₃)₂).

These calculations show that, compared to unsubstubsituted zincphthalocyanine (ZnPc 1), the HOMO/LUMO levels of ZnPc 2 and ZnPc 3bearing a thiophene unit connected with a cyano- or atrifluoromethylacrylate group are shifted downwards to lower energy.Further introduction of methoxy groups at the three benzene unit in ZnPc4 and ZnPc 5 shifts the HOMO/LUMO energy levels upwards. Furtherintroduction of fluorinated residues in ZnPc 6 and ZnPc 7 shift theHOMO/LUMO energy levels again downwards.

In the case of ZnPc 1, ZnPc 4 and ZnPc 5, the LUMO level is above theconduction band level of titanium dioxide (TiO₂). In the case of theother ZnPc's, the LUMO level is under the conduction band level oftitanium dioxide (TiO2). Using titaniumoxy difluoride (TiOF₂), which hasa lower conduction band level compared to TiO₂, it is possible totransfer from the excited state of ZnPc 2, ZnPc 3, ZnPc 6 and ZnPc 7 anelectron to this semiconductor.

Absorption Region

The longest wavelength absorptions (Q band) of phthalocyanines are seenat λ=670-700 nm and of naphthalocyanines at 760-780 nm. By introductionof substituents such as alkoxy groups the longest wavelength absorptionsof phthalocyanines shift to around 750 nm and of naphthalocyanines toaround 860 nm, and extinction coefficients of >10⁵ L mol⁻¹ cm⁻¹.Phthalocyanines and naphthalocyanines described in this patent areabsorbing in dependence on the kind of substituents between 700-750 nmor 790-860 nm with extinction coefficients of >10⁵ L mol⁻¹ cm⁻¹,respectively.

What we claim is:
 1. A compound comprising an element M in a macrocyclicstructure having the following formula (X):

wherein: M is 2H (metal free analogue), zinc (Zn(II)), magnesium(Mg(II)), Al(III)X, Si(IV)X₂, or Sn(IV)X₂ wherein X is selected from thegroup consisting of halides, OH and OR with R being an alkyl or arylgroup; R₁ is H or an alkyl group substituted by at least one halogenatom; R₂ is —CN, —COOH or an alkyl group substituted by at least onehalogen atom; R₃ is independently selected from the group consisting ofH, F, —C_(n)F_(2n+1), —OR′, and —NR'₂; and R₄ are independently selectedfrom the group consisting of H, F, —C_(n)F_(2n+1), —OR′, —NR'₂, andgroups forming an optionally substituted aromatic cycle, adjacent to theexternal aromatic cycles of the macrocyclic structure; with R′ beingindependently selected from the group consisting of H; alkyl groups,optionally fluorinated; and aryl groups, optionally fluorinated. 2-14.(canceled)
 15. A dye-sensitized solar cell, comprising at least acompound according to claim 1 as a dye, said compound being fluorinated,and further comprising at least TiOF₂ as semiconductor.
 16. A method forforming a photoelectric conversion device, comprising using TiOF₂ assemiconductor.
 17. The method according to claim 16, wherein thephotoelectric conversion device is a dye sensitized solar cell.
 18. Themethod according to claim 16, wherein the TiOF2 is in the form ofnanoparticles.
 19. The method according to claim 18, wherein the TiOF₂has a mean primary particle size from 15 to 50 nm.
 20. The methodaccording to claim 17, wherein the dye sensitized solar cell comprises afluorinated dye compound.
 21. A photoelectric conversion devicecomprising a semiconductor layer, wherein the semiconductor layercomprises TiOF2.
 22. The photoelectric conversion device of claim 21,wherein the photoelectric conversion device is a dye sensitized solarcell.
 23. The photoelectric conversion device of claim 21, wherein theTiOF2 is in the form of nanoparticles.
 24. The photoelectric conversiondevice of claim 23, wherein the TiOF2 has a mean primary particle sizefrom 15 to 50 nm.
 25. The photoelectric conversion device of claim 21,wherein the thickness of the semiconductor layer is from 500 nm to 10μm.
 26. The photoelectric conversion device of claim 22, wherein thesemiconductor layer comprises TiOF2 as the sole semiconductor.
 27. Thephotoelectric conversion device of claim 21, further comprising a denseTiO₂ layer on a transparent conducting glass electrode.
 28. Thephotoelectric conversion device of claim 21, wherein the semiconductorlayer is on a transparent conducting glass electrode.
 29. Thephotoelectric conversion device of claim 28, wherein the transparentconducting glass electrode comprises F doped SnO₂ as conductingmaterial.
 30. The photoelectric conversion device of claim 22, furthercomprising a fluorinated dye compound.